My "proudest" use of decorators has been in adding metrics gathering for functions in python, so you'd get automated statsd (and later prometheus) metrics just by having @tracked (or whatever I had its name be - it's been like 7 years) on the function header.

In a sense, that was mutating a global variable by including and tracking the metrics gathering. I imagine this person's early professional exposures to it and need to create their own also came from a similar situation, so "mutating global state" and closures sorta clicked for them.

People learn things by coming to those things from many different entry points and for many different reasons. This is another one of those instances :)